This invention relates to a recording substance and a manufacturing method therefor and a recording method and a recording apparatus (especially a laser beam printer) using this recording substance.
In recent years, the demand for the ability to record not only of course monocolor but also color hard copies of images from video cameras, television and computer graphics and the like has been increasing. Printers using various different recording methods have been developed in response to this and are being deployed in various fields.
Among these recording methods there is one wherein an ink sheet coated with an ink layer consisting of a high density ink dispersed in a suitable binder resin and a body to be transferred onto such as printing paper coated with an ink-receiving resin which receives transferred ink are brought into contact with a fixed pressures heat corresponding to image information is applied by a thermosensitive recording head positioned over the ink sheet, and ink is thermally transferred from the ink sheet to the ink-receiving layer according to this heating.
The so-called thermal transfer method, wherein full-color images are obtained by the operation described above being repeated for each component of an image signal resolved into for example the three subtractive color mixture primary colors yellow, magenta and cyan, is attracting attention as an excellent technology with which printer downsizing and maintenance are easy, recording is instant, and high quality images as good as silver chloride color photographs can be obtained.
FIG. 1 is a schematic front view of a main part of such a thermal transfer type printer. In this printer, a thermosensitive recording head (hereinafter called a thermal head) 1 and a platen roller 3 face each other, and between these an ink sheet 12 consisting of an ink layer 12a on a base film 12b and a paper to be recorded on (body to be transferred onto) 20 consisting of an ink-receiving resin layer (ink-receiving layer) 20a on a paper 20b are pressed against the thermal head 1 in a pinched-together state by the platen roller 3.
Ink (transfer dye) in the ink layer 12a selectively heated by the thermal head 1 is transferred in dot form to the ink-receiving resin layer 20a of the body to be transferred onto 20, and thermal transfer recording is thereby accomplished. For this kind of thermal transfer recording, generally a line system wherein a long thermal head is disposed orthogonal to the paper travel direction or a serial system wherein a thermal head is moved back and forth in a direction orthogonal to the paper travel direction is employed.
The present applicant has already proposed a non-contact type ink-vaporizing laser beam printer (LBP) of the kind shown in FIG. 2 in order to reduce the amount of waste material produced and the amount of transfer energy used and realize a smaller and lighter printer while making the most of the above-mentioned merits of the thermal transfer recording method.
In this printer, a small space 11 in the range lgm to lmm is provided between a recording head (a printer head) 10 having a thermally melting ink layer 22 in a vaporization part 17 and a body to be recorded on (printing paper) 50 having a receiving layer 50 a for receiving vaporized (or sublimed) ink.
By irradiation with laser light L, liquefied ink 22 held in an ink receptacle 37 of the vaporization part 17 of the recording head 10 is selectively heated to near its boiling point and vaporized, this vaporized ink 32 is caused to fly across the space 11 and transfer through a vaporization hole 23 onto the printing paper 50, and an image having continuous gradation is obtained. By this operation being repeated for each component of an image signal resolved into the three subtractive color mixture primary colors yellow, magenta and cyan, full-color printing can be achieved.
With this recording system, preferably the printing paper 50 is made to face the recording head 10 for example from above and laser light L emitted from a laser 18 and focused by a lens 19 is shone into the vicinity of the upper surface of the ink-vaporization part 17 and causes vaporized ink 32 to fly upward. To move the ink through the space 11 by the heating means, besides the vaporization phenomenon, the phenomenon often seen during irradiation with a high output laser that bonds of ink molecules are efficiently broken and using that energy the substance is etched at an extremely high rate, or the phenomenon wherein the energy of a gas produced by boiling or explosion is used to etch the substance at an extremely high rate can be used (these transfer mechanisms other than the vaporization mechanism are called ablation; likewise hereinafter).
An ink reservoir 15 is provided in a head base 14 transparent to laser light, liquefied ink 22 is held between this and a spacer 28 fixed on the head base 14, and the liquefied ink 22 is supplied from here to the vaporization part 17 through an ink supply passage 27. To increase the supply efficiency of ink to the ink-vaporization part 17 and the vaporizing efficiency, fine projections consisting of thin pillars 21 which use the capillary phenomenon to supply and hold ink are provided in the ink-vaporization part 17.
To maintain the above-mentioned space 11 and guide the a printing paper 50 moving in the X direction , a protecting plate 29 is fixed on top of the spacer 28. A heater 16 for maintaining the liquefied state of the ink is embedded in this protecting plate 29, but this kind of heater can alternatively be disposed inside the ink holding part (the above-mentioned passage 17 and ink reservoir 15 ).
A printer head of this kind for a full-color printer has for example ink reservoirs 15Y, 15M and 15C for yellow, magenta and cyan provided in a common base 14, and from there ink of each color is supplied to rows of vaporization parts 17Y, 17M and 17C each forming 12 to 24 dots of the respective color of ink.
Laser beams emitted by a multi-laser array 30 consisting of twelve to twenty-four lasers (especially semiconductor laser chips) 18 disposed in an array are severally focused into the vaporization part s by a microlens array 31 of converging lenses 19.
As described above, in this ink-vaporizing laser beam printer, by sending just the amount of ink which is consumed in recording in a melted state from the ink reservoir to the vaporization part spontaneously or forcibly, or by ink being continuously coated on a suitable base and that base moving to the transfer part, ink can be supplied continuously to the vaporization part. This is possible because the ink contains almost no binder resin. Therefore, because vaporization parts involved in recording can be repeatedly used many times, in contrast to the above-mentioned thermal transfer method wherein the ink sheet is disposable after one use only, this type of printer is advantageous from the resource-saving and environmental conservation points of view.
Also, because this kind of printer uses vaporization or ablation, recording can be performed without the ink layer and the body to be recorded on (printing paper) making contact with each other, and as a result at the time of the second printing or thereafter the kind of reverse transfer and color mixing of ink seen with the thermal transfer system described above do not occur, the only parts heated are in the head including the vaporization parts, and compared to the above-mentioned thermal transfer system power consumption can be markedly reduced. At the same time, because small volume ink reservoirs and not the ink sheet described above are used to supply the ink, the printer can be made small and light.
Also, because this recording system uses ink vaporization or sublimation, it is not necessary to heat an ink-receiving layer of a body to be recorded on as in the thermal transfer method described above, nor is it necessary to press an ink sheet against a body to be recorded on with a high pressure, and in this point also the method is advantageous to downsizing and downweighting of the printer. Because the ink layer of the vaporization part and the body to be recorded on do not make contact with each other, not only is it impossible for thermal fusing to occur between them, but also recording is possible even when the compatibility of the ink and the receiving layer resin is poor. As a result, the freedom of design and selection of the ink and the receiving layer resin markedly widen.
Also, as a heat energy supply source for vaporizing (or subliming) the ink, the semiconductor lasers 18 are used as light sources, and because semiconductor lasers have high conversion efficiency from electrical power to light and also have excellent directivity and convergence, the efficiency with which they transmit heat energy to ink is very high. Therefore, compared to conventional types (the above-mentioned transfer by thermal head and ink jet, etc) they also have the merit that their energy use efficiency is markedly high and they are advantageous to miniaturization and power consumption reduction.
Also, although with conventional ink jet type color printers tonal expression is difficult, because control of output power and pulse width etc of semiconductor lasers is easy, with the recording method described above, multi-tonal expression can be easily realized. That is, it is possible to convert an electrical image made by a color video camera or the like into ink transfer according to an image signal with semiconductor lasers and form a full color image equal to a silver chloride photograph having at least 128 tones per color.
As a transfer body suitable for this ink vaporization recording method, it is preferable that the head 10 be amply able to withstand the heat applied instantaneously during transfer and have a structure wherein thin pillars 21 of for example several lm in size of which the surface area for supplying liquid ink spontaneously using the capillary phenomenon to the vaporization part (transfer part) is large and which can hold ink firmly even during transfer be provided. Also, by providing a heating device, it becomes possible to use an ink or ink mixture whose melting point is above room temperature.
As an ink suited to this recording method, any kind of ink which has a suitable vaporization rate or ablation rate, shows a fluid state at under 200.degree. C. in a simple or mixed state, and has the necessary resistance to heat may be used. Specific examples include dispersion inks, oil-soluble inks, basic inks and acidic inks. In particular, when the ablation mechanism is more dominant than the vaporization mechanism, transfer is possible even with inks of high molecular weights and whose vaporization rates are low like direct inks and carbon black and pigments. Even with an ink whose melting point is above room temperature, by mixing inks or mixing an ink with a volatile low molecular weight substance, the melting point falls.
Also, as printing paper suited to this recording method, any kind of printing paper having a suitable affinity for the ink and which easily receives the ink and promotes the original coloring of the ink and has the action of fixing the ink may be used. For example, for use with a dispersion ink, a paper having its surface coated with polyester resin, polyvinylchloride resin, acetone resin or the like having good affinity with the dispersion ink is preferable. The fixing of ink transferred to the printing paper may alternatively be effected by a system wherein the image after transfer is heated and the ink on the surface is thereby caused to permeate into the receiving layer.
Heating means of ink transfer systems can be generally divided into methods using thermal heads and methods which combine laser light and a material which shows absorption in a wavelength region including the laser light wavelength region and converts light energy into heat energy (a photo-thermal convertor).
When laser light is used, there are the merits that the resolution increases markedly and by making the laser light density large with an optical system concentrated heating becomes possible and the arrival temperature rises and as a result the thermal efficiency increases. In particular, by using a multilaser, the time taken to transfer one picture is greatly reduced.
However, the photo-thermal convertor must be one which is heat-resistant enough to continuously absorb the light energy of the laser light. Therefore, as a photo-thermal convertor used in this method, besides directly providing the transfer part with a thin film light-absorbing body such as a metallic thin film showing absorption coinciding with the wavelength of the light emitted by the lasers or a two-layer film of a metallic thin film and a ceramic thin film having a high dielectric constant, materials or inks with good resistance to heat like fine particle type light absorbers such as carbon black or metal fine particles, organic inks or organic metallic inks such as phthalocyanine inks, naphthalocyanine inks, cyanine inks, anthraquinone inks uniformly dispersed in an ink may alternatively be used.
The present inventors discovered that when performing heat transfer by the ink-vaporizing recording method described above, when impurities other than ink components and necessary additives (antioxidants, radical inhibitors, infrared absorbers, plasticizers or melting point lowering agents or the like) are included in the recording substance which is the transfer coloring material, these kinds of impurity sometimes do not vaporize or ablate and remain on the transfer part of the transfer body as solids, and this kind of solid causes clogging of the transfer body, sensitivity decrease and reduction in tonal reproducibility are seen, and in some cases it becomes impossible to obtain a high quality image.
As a result of sampling and analyzing this kind of solid, it was found that this residual solid is [1] thermal decomposition products of ink or necessary additives, [2] thermal decomposition products of substances other than ink or necessary additives, [3] nonvolatile substances other than ink or necessary additives.